The shell or “capsid” of a virus is made of protein and is intended to protect the DNA in the virus when it attacks another cell. The structure of these capsids is well understood, but very little is known about their mechanical properties.

Wuite and co-workers started by placing the sharp tip of an atomic force microscope (AFM) onto the shell of a bacteriophage – a virus that infects bacteria. Next, they slowly increased the force applied by the tip and recorded how the shell deformed. They operated the AFM in a so-called “jumping mode”, which allowed them to carefully control the maximum force exerted on the shell.

From these measurements, Wuite’s team calculated that the shell had a Young’s modulus of 1.8 gigapascals, which is comparable to that of hard plastic. Moreover, they found that the shells could withstand forces of several nanonewtons and could be flattened by up 30% of their original height without cracking. “It came as a surprise to us to find that the bacteriophage capsid was as strong as it was,” Wuite told PhysicsWeb.

“From a medical point of view, this research might reveal new insights into the transport strategies of different viruses and the shell strength might also relate to the time a virus stays infectious outside a host cell,” said Wuite. “From a nanotechnology point of view, viral capsids could be used as nanocontainers which are strong and able to self-assemble. The capsid proteins could also function as building blocks to make other complex structures.”

The team is now investigating other viruses using this technique.